An image processing device comprises an encoder for encoding inputted image data in the form of fixed length compression. The encoded data encoded in the form of the fixed length compression by the encoder is stored in a hard disk through an encoded data buffer which is a toggle buffer. Accordingly, the image data can be stored in the hard disk at a constant speed, and a capacity of the encoded data buffer can be minimized since the data amount after data compression is decided. As a result, it is not necessary to provide a semiconductor memory corresponding to storage of one screen, so that a low cost image processing device is obtained.